President Joe Biden said the US will respond to an Iran-backed attack on its forces in Jordan, after he announced the news that three US troops were killed.

"We shall respond," he said at a campaign event in South Carolina, asking for a moment of silence. Biden earlier blamed Iran-backed groups for the attack that occurred Saturday night.

“While we are still gathering the facts of this attack, we know it was carried out by radical Iran-backed militant groups operating in Syria and Iraq,” the President said in a statement released by the White House.

At least 34 personnel were being evaluated for possible traumatic brain injury, a US official told Reuters.

"While we’re still gathering facts, this is most assuredly the work of an Iranian-backed militia group," a second official said.

US lawmakers began to react to the news by demanding a tough US reaction to what they see as a major escalation by Iran.

US Senate Republican Leader Mitch McConnell (R-KY) issued a statement, urging the President to be decisive. “Last night, the cost of failure to deter America’s adversaries was again measured in American lives. We cannot afford to keep responding to this violent aggression with hesitation and half-measures," the statement reads.

Senator Tim Scott (R- S. Carolina) issued a tweet saying, "The Biden administration’s appeasement of Iran must end. It’s time for clear and decisive action, and Iran must be held accountable for the malign activities of its proxies."

Senator Dan Sullivan of Alaska fired off a tweet saying, "The President needs to order a clear, lethal and overwhelming response that demonstrates to Iran and to the world that whoever targets our men and women in uniform—or supports these attacks—will face the full might of the U.S. military."

The deaths marked the first fatalities of US troops in the region since war began in Gaza. Biden said the attack occurred on Saturday night. Iranian backed proxy militia forces have launched more than 150 attacks in Syria and Iraq targeting US forces since mid-October.

The attack is a major escalation of the already tense situation in the Middle East, where war broke out in Gaza after Palestinian Islamist group Hamas' attack on Israel on Oct. 7 which killed 1,200, mostly civilians.

Thousands have also been killed in the subsequent Israeli military operation in Gaza, although there is no independent and reliable figure.

While Iran has avoided direct military involvement in the Gaza war, its strategy seems to be using proxy forces to harass the US and Israel.

Iran International reported on Saturday that according to a diplomatic source, the Biden administration is discussing with European allies a scenario to increase sanctions on the Islamic Republic. Iran’s aggressive regional policies since October seems to be the reason the White House has decided to adopt a tougher stance against Tehran.

The US has launched a few retaliatory attacks against militia forces in Iraq and Syria, but the attacks have continued. Critics of President Biden’s Iran policy argue that the United States should directly target Iranian interests to deter Tehran’s proxies.

Iranian backed Houthi forces in Yemen have also launched dozens of missile and drone attacks against commercial vessels and Western warships in the Red Sea area. Commercial maritime traffic has suffered as a result.

While the United States has thus far maintained an official line that Washington is not at war in the region, and does not seek escalation, it has made strikes against targets of Yemen's Houthi forces.

"We will carry on their commitment to fight terrorism. And have no doubt - we will hold all those responsible to account at a time and in a manner of our choosing," Biden said in his statement released by the White House.